Method of operating gas turbine engine with fan damage

Abstract

Normal high load operation automatically varies nozzle area to maintain an optimum engine pressure ratio (EPR). An error signal representing fan damage is established by comparing the actual EPR to the predicted EPR. Compressor stalls are also monitored. In response to these signals a minimum nozzle area is set and modified. Automatic operation to hold EPR and afterburning is inhibited. Further signals representing satisfactory operation may reset the inhibiting action.

We claim: 
     
       1. A method of operating a gas turbine engine in a manner to accommodate fan damage comprising: determining an actual EPR signal;   establishing an EPR error signal by comparing said actual EPR signal to an anticipated EPR signal;   establishing a fan damage signal, by comparing said EPR error signal to a tolerable EPR fan damage error, when said EPR error signal exceeds said tolerable EPR fan damage error;   comparing said EPR error signal to a pre-established nozzle area versus EPR error ratio relationship representing predicted stall limit with fan damage;   determining the presence of an immediately preceding stall; and   limiting the minimum area of the engine nozzle to a corresponding pre-selected nozzle area in the presence of both said fan damage signal and an immediately preceding stall.   
     
     
       2. A method as in claim 1 comprising also: comparing said EPR error signal to a tolerable EPR sensor error; and   nullifying the step of limiting the minimum area when said EPR error signal is less than said tolerable EPR sensor error.   
     
     
       3. A method as in claim 1 comprising also: detecting a subsequent stall;   ratcheting the minimum area of said nozzle to a higher value in response to said subsequent stall.   
     
     
       4. A method as in claim 1 comprising also: inhibiting augmentation of said engine in the presence of both said fan damage signal and an immediately preceding stall.